The invention relates to a method for parameter estimation in a digital radio system receiver comprising a detector generating a number describing the probability of a symbol received using soft decision metrics.
The invention further relates to a digital radio system receiver for desired parameter estimation comprising a detector for generating a number describing the probability of a symbol received using soft decision metrics.
In radio systems a channel estimate is a set of parameters, or a vector, which can be generated using various algorithms. The channel estimate is needed, for example, in different radio system detectors for detecting a received signal. The channel estimate is usually generated using a training sequence or the like, whereby, for example in the GSM system, the training sequence is correlated with received samples. Prior art algorithms often utilize Least Square Problem. A common Least Square Error Problem can be solved by using a Kalman filter, an extended Kalman filter, a Recursive Least Square and a Least Mean Square. Typically these algorithms are designed for parameter estimation, where predetermined data is available, but there are also algorithms intended for Blind Equalization, such as the Expectation Maximization algorithm. The channel estimate is not a constant at different times but changes continuously. Thus the channel estimate generated using a training sequence is not necessarily suitable for data detection.
U.S. patent publication 5,263,033 represents prior art and is incorporated herein by reference. In the solution of the publication preliminary symbol decisions are fed back to the LMS algorithm in order to specify the channel estimate during the calculation of the Viterbi algorithm trellis. A problem with this solution is that in order to specify the channel estimate preliminary or actual decisions are needed that may either be correct or incorrect ones. Consequently, when the decision is incorrect the channel estimate is incorrectly corrected which leads to a poorer final result than was expected in the received signal processing.
It is an object of the invention to provide a parameter estimation method and a receiver implementing the method so as to solve the above problems and to be able to correct a parameter estimate without preliminary or final decisions.
This is achieved with the type of method described in the preamble characterized by generating a mean value of the numbers describing the probability of a received symbol and generating a new channel estimate as a parameter utilizing the mean value.
The receiver of the invention is, in turn, characterized by comprising means to estimate a channel estimate utilizing a mean value generated from the numbers describing the probability of a received symbol produced by a detector, and the detector being arranged to estimate a desired parameter using the generated channel estimate.
The method and system of the invention provide several advantages. The solution avoids using symbol decisions and at the same time avoids correcting a parameter estimate together with incorrect decisions. The solution also improves the sensitivity of the receiver since the estimated channel estimate will be better. The solution can also be used as an in-built Doppler equalizer of the receiver.